Engineering heterologous iron siderophore complex utilization in rhizobia: Effect on growth of peanut and pigeon pea plants

Cloning and expression of two siderophore receptor genes, pfeA, and fpvA of Pseudomonas aeruginosa origin, encoding outer membrane receptor for enterobactin, a catechol type siderophore and for pyoverdin, a mixed ligand type siderophore, respectively, were studied in two Cajanus cajan rhizobial isolates, IC3123 and ST1. Expression of an approximately 80/89 kDa protein band was seen in all the transformants while the corresponding parental strains failed to express the same. Functionality of the construct, pAKEnt (plasmid containing pfeA) and pAKFpvA (plasmid harbouring fpvA), was checked by transforming it in P. aeruginosa K407Δ pfeA and P. aeruginosa K437Δ fpvA, respectively and monitoring phenotypic complementation. Positive cross utilization of cognate siderophores by respective transformant and failure to utilize the same by corresponding parent strains, confirmed the expression of the respective genes. The constructs, pAKEnt and pAKFpvA, were mobilized in to Rhizobium sp. strains IC3123 and ST1 and expression of the corresponding gene in transformants led to utilization of the respective siderophores and stimulation in the growth of the transformants in the presence of respective siderophore producing strains in a co-inoculation study. Peanut and pigeon pea plants inoculated with transformants harbouring pAKEnt and pAKFpvA constructs, not only showed better rhizospheric colonization but also showed better plant growth with respect to increase in root weight, shoot weight, nodule number and chlorophyll content as compared to the parental strains. Amongst the two constructs, pAKEnt showed relatively higher increase in growth response as compared to pAKFpvA, which could be attributed to higher affinity of enterobactin for Fe3+ (K = 1052 M−1) as compared to pyoverdine (K = 1032 M−1).

► Heterologous expression of outer membrane siderophore receptor genes pfeA and fpvA in bioinoculant rhizobial strains.
► Effect on growth and cross-utilization of siderophore on rhizobia.
► Effect on growth parameters of Cajanus cajan and Arachis hypogea plants due to heterologous expression of pfeA and fpvA genes.